1. Technical Field
The present disclosure relates generally to the treatment of respiratory conditions with the delivery of pressurized flow of breathable gas to a patient and more particularly, to a continuous positive airway pressure (CPAP) target pressure comfort signature that naturally adapts blower pressure to patient breathing by measuring comfort directly from the source, e.g., measuring pressure at the patient airway.
2. Related Art
Sleep apnea is a serious medical condition in which patient breathing during sleep pauses abnormally, or is abnormally low. Apnea is categorized as obstructive, central, and combined obstructive and central, though the obstructive sleep apnea (OSA) is the most common. The patient's upper airway repeatedly narrows or collapses, causing pauses in breathing that may extend in duration up to half a minute. Although some degree of apnea is considered normal, in more severe cases, daytime sleepiness and fatigue may result as a consequence of reduced blood oxygen saturation, as well as constant interruptions to sleep cycles resulting from patients gasping for air. There have been studies linking sleep apnea to more severe long-term health issues including heart disease and depression, and recently, to cancer as well. With apnea being strongly linked to obesity, and with obesity being projected to increase, the number of patients suffering from sleep apnea is likely to increase concomitantly.
One common treatment for obstructive sleep apnea is continuous positive airway pressure (CPAP) therapy, where a positive pressure is applied to the patient to prevent its collapse as would otherwise occur during an apnea episode. By retaining the patient's airway, normal, uninterrupted breathing during sleep is ensured. In a basic implementation, CPAP therapy applies a constant pressure that is not tied to the patient's normal breathing cycle. The positive airway pressure is desired in the inspiratory phase when the pressure differences between the lungs and the nose contribute to the collapse of the intermediate airway. Earlier patient breathing assistance devices tended to be uncomfortable to use because of the bulkiness associated with the patient interface, as well as the misapplication of pressure resulting from sub-optimal control methodologies. Various improvements have been developed to reduce discomfort during therapy, particularly at critical points along the patient's respiratory cycle. Thus, what was previously prescribed only for the more severe cases of sleep apnea in which the benefits of treatment outweighed the significant discomfort is now useful for treating a wider spectrum of sleep apnea conditions.
Adherence to CPAP therapy is difficult for some patients with obstructive sleep apnea and especially for those who have difficulty exhaling against a constant pressure at the mask that they need to wear at night while sleeping or attempting to sleep. Many patients describe the experienced sensation as being akin to asphyxiating. Furthermore, to maintain airway patency and thus treat OSA, positive pressure is only needed during the end of exhalation to the beginning of inhalation, at which time this positive pressure acts a pneumatic splint to hold the upper airway open. Based on this finding, several technological advancements have been developed including bi-level pressure and pressure relief.
In bi-level CPAP therapy, two pressures are used during patient's breathing cycle: a high pressure during inspiration, normally called inspiratory positive airway pressure (IPAP), and another lower pressure during exhalation, normally called exhaled positive airway pressure (EPAP). One advantage of this technique is that the patient feels the device is synchronized to their breathing, which elevates their degree of comfort. However, bi-level CPAP therapy suffers from a major disadvantage, namely, that in order to implement the feature in hardware more costly components than a regular CPAP system are required. Cost issues are a serious concern in the development and marketing of CPAP systems, as they are intended for purchase by the end-user patient.
A more recent and less costly solution to relieving pressure during exhalation to improve patient comfort is the development of pressure relief technology. The broad concept is to detect inspiration and exhalation phases of the breathing cycle, and at the time of exhalation, relieve pressure momentarily either in accordance with the shape of the patient's airflow rate and/or disengaging power to the blower at the beginning of inhalation. Both of these techniques rely on a flow signal to determine the timing of pressure relief. However, the use of a flow signal suffers from various deficiencies as well, and as such may not achieve the highest possible degree of comfort.
Existing systems are generally limited to guessing what comfort is needed based on flow signal, and provide “relief” accordingly. Accordingly, there is a need in the art for a CPAP target pressure comfort signature that naturally adapts blower pressure to patient breathing by measuring comfort directly from the source.